What do the results mean?
The main purpose of a CT scan performed in the hours after stroke is to determine if your symptoms are due to a blocked-vessel stroke or if there is bleeding in the brain. For patients who seek treatment within a few hours of symptoms, ruling out bleeding with CT means you may be eligible for treatment with the first-choice drug for treating stroke: tPA.
A CT scan can be used to rule out bleeding, but even if it does not show a blockage, that does not necessarily mean you haven't had a blocked-vessel stroke. Sometimes the brain changes caused by a stroke will not be visible on the CT scan until several hours after the stroke occurred. The stroke might also be too small to see on the CT scan, or it may be located in an area of the brain the CT scan does not see well, such as at the base of the brain in the cerebellum or brain stem.
CT scan results can determine if tests that are more detailed are necessary to look at the vessels in the brain, such as an angiogram. When used as a screening test, CT scans with contrast dye can detect narrowing of the blood vessels that may cause problems in the future, in time to start treatment to prevent a stroke or TIA.
What are the risks of a CT scan?
The CT scan is a safe and painless procedure. Some people have an allergic reaction to the dye used for a CT angiogram or perfusion CT, although this is rare. Be sure to tell your doctor ahead of time if you have experienced this in the past--medications can be given during the procedure to minimize this problem. Because it uses X-rays to produce an image, CT scans expose you to some radiation. The amount of radiation you are exposed to during diagnostic tests is considered safe. The benefits of the test far outweigh any potential risks, and the technicians are trained to minimize your radiation exposure. For information on radiation safety, see the National Institutes of Health Radiation Fact Sheet.